THE LAY-OUT OF ROADS IN RELATION TO REQUIREMENTS

Progress, Volume XI, Issue 9, 1 May 1916, Page 620

THE LAY-OUT OF ROADS IN RELATION TO REQUIREMENTS

W'Ax By S. D. ADSHEAD, Professor of Town Planning in Liverpool University, /s] from the “ Town Planning Review.”

It is about 15 years since the motor-propelled vehicle appeared, offering new problems for the designer of the public way. Its introduction had, however, been anticipated some years previously, the Great Horseless Carriage Company having commenced the construction of autocars in this country as a sound venture, notwithstanding that at the time the law required every self-propelled vehicle to limit its speed to five miles an hour and be preceded by a man waving a red flag. To-day the volume of self-propelled vehicles everywhere preponderates over that drawn by a horse, and except on secondary roads of purely local interest, the use of the road by horse-drawn vehicles is everywhere subsidiary, and indeed it is but too true, though perhaps sad to announce, that the quicker the horse is banished from the road the safer will it become for the preponderating motor traffic. Perhaps one of the greatest difficulties the motorist has to contend with in driving, is judging negotiations with innumerable types of vehicles proceeding at variable speeds. Let us then first direct our attention to road requirements from the point of view of the driver of the motor-propelled waggon and car. We will then be in a better position to deal with direction, grade, and construction: questions more intimately connected with the actual design of the road. As already stated, roads are to-day used by a great variety of vehicles, and amongst those of th selfpropelled type alone, may be mentioned such an assortment as the bicycle, the light car, the van, and the 3-ton waggon. In considering the capabilities of the lighter types and their use of the road, what appear to be dangerous conditions of driving to the man who has never driven, will often be found not to be so to the man who has driven say ten thousand miles.

He who has had but little experience of motoring regards excessive speed as in itself constituting the one danger and evil to be avoided, whilst he who drives, soon realizes, that with limitations, excessive speed, as such, does not necessarily constitute a danger. Danger in motoring both to the motorist and to other users of the road is caused by innumerable factors contingent upon bad road planning, bad road construction, the lack of a standardised system of road warnings, and bad design in the arrangement of curves and crossings. An ordinary car can traverse a straight road having an even surface and bordered with wide margins at a speed of 25 miles an hour and even more with perfect safety. In fact I would go so far as to say that when we get perfectly constructed main thoroughfares between towns

whose curves do not exceed a radius of say 400 yards, a speed of 25 miles an hour, and not 20 as at present, is a perfectly safe limit to impose. It is not generally realized that a car, both economically and as regards comfort in travelling, is doing its best when attaining a tolerably high speed. Many of the more powerfully built chassis do not run quite freely until a speed of from 20 to 30 miles an hour or even more has been attained. The Ford car, of which there are so many on the road, seems to be running in its happiest vein at a speed of about 25 miles an hour, though this car, together with other makes of about 15 horse-power and under, can well break into a speed of 30 miles an hour without undue strain. But it must be remembered that these high speeds can only be maintained with case and safety under the very best conditions of road surface, road direction, and an exact observance of road regulations. Experience proves that on the open road of to-day, notwithstanding the regulations laying down speed limits, the average pace of the motor-car is from 20 to 25 miles an hour, and in the country town, the average speed of the passing car is quite 15 miles an hour. The speed limit is consistently exceeded. it is not generally appreciated that the tendency of motoring is to take light hills at a higher speed than when coming down, it being better for the engine to proceed on a high gear when it can do so. The ascent of a hill offers better opportunities for the sudden application of the brake control, and thus a high speed up-hill can be maintained with greater safety than when descending. But the conditions of fast travelling always require that the road be open and that the view ahead be at all times unobstructed, and such that a reduction of speed can be undertaken gradually, and so as not to jar the car with the too sudden application of a brake, which on a wet or greasy road will almost certainly result in a dangerous side slip, A too frequent application of the brakes very rapidly wears both tyres and brake bands, a fact well known to the driver who is responsible for his own repairs. It is a credential of good driving that judgment in slowing up be so accurate that the application of a brake is not required, until the car has practically stopped. But favourable conditions for speed are influenced by road construction. The nearer the cross section of a road approaches the horizontal line, the safer it is as regards skidding. It is also extremely unpleasant to drive on the deflected side of a highly cambered road; too steep a camber makes nicety of steering very difficult. It may also be mentioned that tram lines, are very annoying and cause the

same trouble. When the wheels of a car get on to a tram line there is always an element of uncertainty as to whether the car can be turned out without something of a shock. When tram lines are wet a too sudden application of the wheel will almost surely result, if not in the overturning of the car, in at any rate a serious skid or dangerous twist into the side of the road. Greasy asphalte and slightly wet wood block convert driving into something approaching sliding, nothing but the perfectly straight line being possible under such conditions, and that at a pace not exceeding five miles an hour. Were road traffic confined to light cars, light delivery vans, and bicycles, the more difficult problems in road construction would at once be eliminated, but as practically all main traffic thoroughfares have in addition to be so constructed as to take very heavy engines and waggons the problem of construction becomes very difficult. As regards the driving of heavy waggons, road requirements are in this case quite different from those best suited to the light car, but one of the greatest dangers that beset this class of traffic is that of skidding. Grease and mud of a clayey nature render all movement absolutely impossible, and when hills occur or where the camber is great with a declivity at the side of the road, a frightful catastrophe is more than a possibility. But with this class of traffic, given a hard and gritty surface, the perfectly straight road free of all obstructions is not so necessary as in the case of higher speed traffic.

It has been mentioned that essentials of easy travelling for the more rapid class of vehicle are freedom from sharp curves, a very slight camber on the cross section, and wide open spaces at cither side of the road, but there is also another requirement smoothness of surface with perfect grip. _ Of the many kinds of surfacing at present met with, including granite sets, wood block, tar and water bound macadam carpeted with bituminous asphalte or tar spread, by far the best is wood block, if dry. On the whole wood block in good condition offers the most even surface and the smoothest face. A carpet of asphalte, bituminous or otherwise, where subjected to the heaviest traffic having solid tyres, invariably works into waves. In point of fact, except as regards its freedom from dust, it is rare to find an asphalte track that can offer such smooth running as a good water bound macadam. It may be mentioned, however, that this is probably largely due to the fact that most of our existing water bound macadam roads are secondary roads not used by heavy traffic. It is the heavy traffic that is the great destructor of roads. Very few of our main roads as at present constructed were ever intended to resist the extraordinary weights there are to-day put upon them, and one of the conditions to be observed in the construction of the main road of the future will be to provide a greater increase in the strength of the road foundation.

The undulations which occur on the surface of nearly all main roads as we find.them to-day are produced by heavy traffic on a slight foundation. But

for heavy traffic not only is there required extraordinary strength in the foundation or bottom, but also there will need to be devised some surface treatment less porous and flimsy than tar-sprayed or even asphalte-finished macadam. The effect of heavy traffic on a tar-sprayed or even asphalte-coated surface is very quickly to pick it up and wear it into holes, which as water enters soon become enlarged and set up a breaking away of the foundation. A bituminous asphalte is less liable to pick up than an asphalte composed of cheaper ingredients, but this in hot weather is subject to roll into waves. It is no doubt impossible to keep heavy vehicular traffic off the main thoroughfares, and new methods must be devised to contend with the difficulties they create. i '

In some cases heavy traffic can be moved into special tracks, constructed with sets on a concrete foundation, but generally it will have to be assumed that main roads are to be constructed for both light and heavy traffic. In my opinion when there is such traffic nothing but a very strong foundation, either of reinforced concrete, or where the sub-soil is gravel or of an equally solid nature, 12 inches of matrix surfaced with 4 inches of tar-bound macadam and coated with a bituminous sheet will preserve a good surface and remain reasonably durable. On steep hills a paved track on concrete at either side of the road for the use of heavy traffic may prove advantageous. There is evidence, however, for assuming that before long the solid tyre, even in the case of heavy vehicles, will be abandoned for the pneumatic, and thus give a much longer duration to the life of a road.

We have said nothing as yet as regards the width of roads. It may be stated at the outset that the usual method of deciding the width of a road by multiples of 8 feet in fallacious, if it is assumed that 8 feet is the necessary width for a single stream of traffic.

Where the pace does not exceed say 10 miles an hour, as for instance in the busiest street of a town, it is correct to assume that 8 feet will be required for each stream, but in main thoroughfares outside towns it must be remembered that a factor to be considered is (besides the passing) the overtaking of a car which in an open road (and where conditions of surface do not dictate a particular track being followed) usually occupies a position some 6 feet from the edge of the road. It must also be remembered that, in overtaking, much more hpace is required than in passing. One car overtaking another always requires, if it is not to be slowed down, at least 4 feet of free-way to allow for any unforeseen deflection on the part of the car to be passed. So that the main road which is designed to take three rows of cars should be at least 30 feet in width and not 24, as is usually stated. But in the main thoroughfare between towns it is very infrequent that three cars are so timed as to pass at the same place, and as a narrow road with, a good surface is preferable to a wide road badly constructed, in ray* opinion it is far better to have main thoroughfares outside towns and suburbs 20 feet

rather than 30 feet wide. They should, however, nowhere be less than this figure. Having regard to questions of economy 20 feet should be the standard width for a main thoroughfare between towns. Immediately outside the built up area of a town a width of 30 feet is ample, and in the built-up streets, so as to allow for standing vehicles, 45 feet between the kerbs is for ordinary streets very good. Streets made wider should be separated into divisions for fast and slow traffic, cycles, &c, both for the better direction of the traffic and also for the safety of the pedestrian when crossing.

Having now dealt with the road from the point of view of its direction and construction in relation to the requirements of motor traffic, let us consider for a moment its influence on the town and country through which it has to pass. It may at ence be stated that in a residential suburb which is connected with the tow by a railway, the main traffic route is altogether an evil, and in any case so longas such a suburb is connected with a main road system by a good secondary road it is to its interest to be situated quite apart from a main road. Even the residential suburb, which depends upon the motor bus or tram for access to and egress from the city, is placed in the best relation to it when it passes immediately outside it, not through it. Indeed, the main traffic route, unless it is bordered with a parkway, is as destructive to the. interests of a residential district as is a railway line. Consequently, when planning main roads it is best to avoid the centre of districts which are likely to become popular residential areas. In the ideal planning of a district both railways and main roads would be • outside rather than through residential districts. It might be of interest here to recite the resolution of the Third International Road Congress with reference to this. It was as follows —

“As a general principle it is better that new main roads be constructed to pass outside rather than through towns, and when an existing main road passing through a town is unsatisfactory for through traffic,, it is often better, in preference to widening an existing narrow main road through the centre of a town, to construct a new one outside. New roads should be planned according to the principles of the science of Town Planning.” We would, however, point out that the application of this resolution is exclusively advanced, with a view to safety as regards the townsfolk and convenience as regards the motorist. However, at times it is best to take the traffic right through the centre

of a town. A motorist likes to do his journey in stages, and does not mind slowing down say at intervals of 10 miles. It relieves him from the monotony of a too-continuous run at high speed, and adds interest to his journey to pass through a town. But the new town designed for this should have parkways where there arc houses, and at least 45 feet between kerbs where there are shops.

We now come to the question of gradients. In the first place, it must be remembered that the steepest gradient which may be allowed for horse-drawn

vehicles is necessarily much less than that which can easily be negotiated by motors. All cars can easily surmount a 5 per cent, gradient on a high gear, and if the conditions of surface are good, most cars will ascend a 10 per cent, gradient on top speed. Therefore, whilst for motor traffic, as for other traffic, it is best where possible to keep the gradient low, a 10 per cent, gradient need not be regarded as impracticable. But the question of a satisfactory gradient is one which to the motorist is intimately connected with other issues, such as the length of the hill and the straightness of the road. To light cars, a straight road with a series of short steep hills forming a switchback track offers very littlemore resistance than the level road, the reduction of engine power and impetus attained in the downgrade almost completely compensating for the extra power required in the upgrade. The worst form of road for the motorist is that in which there occur sharp curves, sometimes becoming almost hairpin corners on a steep grade. Here, in the case of the right-hand ascending curve, where possible, there should be a wide grass margin on the left. Indeed, the planning of a wide grass margin on the outer edge of all sharp curves, both on the grade or level, is a provision for safety not generally appreciated. The tendency of all motorists when rounding curves is to keep on the outer edge of the curve, and experiences are endless where motorists ascending hills on the outer side of a curve have suddenly observed a descending car appearing at top speed on the wrong side of the road. It need hardly be mentioned in this connection that with round sharp curves it is an added advantage to slope the whole of the road towards the inside in its cross section.

As yet nothing has been mentioned about cross roads. There exists to-day two schools, each with a different view as regards this. The one advises the placing of all roads entering a main road in such a position as is not opposite another road; in other words, cross roads are everywhere to be avoided. Others make no particular effort to plan in this way; indeed, preferring a straight course in every direction, they depend upon standardized rules being adhered to in the use of the road, and features such as islands and refuges for the prevention of collisions. Surely it ought not to be always necessary to take a zigzag course when crossing a main thoroughfare, and all- things considered it is best to run roads across one another.

But in this connection the importance of in some way clearly marking the entrance to a main road cannot be over-emphasized. It is absurd that motorists when going ahead on a main road should, as is almost always necessary at present for absolute safety, be required to pull up at every cross road. Without exception, on the left side of every secondary road, at least 50 yards before it enters a main road, there should be a fixed sign, bearing the inscription in clear letters, "Main Road." There are innumerable cross roads of equal importance; the Local Authority or County Council should decide as and the secondary road should be labelled accordingto which is to be regarded as of prior importance,

ly. It is ridiculous that dangers and directions should be notified in such a variety of terms as one finds them to-day on main roads. The "speed limit" caution on entering a built-up area, and the "School" caution are excellent, but the "Cross lload" caution and the "Concealed Turning" as notifications are not standardized directions. With secondary entering roads labelled on a universally standardized system the need for such labels on main roads would be unnecessary.

Finally, no motorist should be allowed a license until he has passed an examination on the elemental rules of the road, and one of the most stringent should be that every vehicle must draw up dead on entering a main road. There are other points that occur to the road planner which are only discoverable after considerable experience as a user of the road. Three may be mentioned: Where lamps on one side of the road only are employed, they should under no circumstances whatever alternate at intervals from one side of the road to the other. On a dark night the line of the lamps often provides the only means whereby the direction of the road is indicated, and where they cross the road on a very dark night the motorist almost invariably finds himself mounting the kerb, if no worse. Another point worth mentioning is that on the open road the tendency of the driver of the car is to occupy a position on the road which is very slightly to the left of the centre. He is not so inclined to keep entirely to the left as is the driver of a horse-drawn vehicle. He does this to obviate the camber, to make steering easier, and to be as far from the edge of the pavement as possible to avoid unsuspecting people and animals stepping out on to the road. This being so, the middle of the road for a space of 8 to 10 feet should he regarded as that part of the road best worth repairing, and where repairs and the making good of holes is being carried on it is better to execute in the first instance two miles of this strip than one mile of the whole road. The third point to which attention should be directed is the importance of so designing roads that the necessity for flexibility of direction in driving is, wherever possible, avoided, and in this connection the obstructive nature of central lamp standards and car poles cannot be over-estimated. The tendency of motor traffic is to go much quicker and in a much straighter line than horse traffic, and if these were obstructive and dangerous in the old days, they are ever so much more obstructive and dangerous to-day.